[IslamElsayed]

Fixes #1536.

The bug

With use_parent_strategy on (the default), building a factory that has an association calls @build_strategy.to_sym unconditionally:

strategy_override = overrides.fetch(:strategy) {
  FactoryBot.use_parent_strategy ? @build_strategy.to_sym : :create
}

A strategy only has to implement #result and #association — #to_sym is something the five built-in strategies happen to have. Any custom strategy without it raises:

NoMethodError: undefined method `to_sym' for an instance of #<Class:0x...>

@composerinteralia called this an unintentional breaking change on the issue and wrote out the fix; it was never implemented, and the only PR on the thread (#1537) was docs-only.

The fix

His suggestion, falling back to the strategy's class. That works because Strategy.lookup_strategy already returns a Class unchanged:

def self.lookup_strategy(name_or_object)
  return name_or_object if name_or_object.is_a?(Class)

  FactoryBot::Internal.strategy_by_name(name_or_object)
end

so the association is built with the same custom strategy as its parent — which is what use_parent_strategy is asking for.

One deliberate deviation: I inlined the condition rather than extracting it into a private method. Evaluator defines a factory's attributes as singleton methods on itself, so adding an instance method risks shadowing an attribute that happens to share its name.

Testing

An acceptance example in register_strategies_spec.rb registering a strategy that implements #result and #association but not #to_sym, and asserting the association is built. Before the fix it fails with exactly the NoMethodError from the issue.

I checked it isn't vacuous by breaking the fix two ways: restoring the unconditional to_sym fails it, and returning :create from the fallback instead of the class also fails it — so it pins that the association uses the custom strategy, not merely that nothing raises.

Full suite: 775 examples, 0 failures. standardrb clean on both files. Run under Ruby 3.3.5 rather than the 4.0.1 in .tool-versions, since the gemspec allows >= 3.0.0.

I have not added the deprecation @composerinteralia mentioned for eventually removing the fallback — happy to if you want it in the same PR.

Disclosure: I use AI assistance when working on patches, and I check and test everything before submitting.